Fluid recirculating economizer

ABSTRACT

A flue gas heat recovery device is described. The device includes a packing tower. The packing tower is adapted to receive a flue gas stream. The packing tower also contains at least one water inlet, a water collection reservoir and a packing tray positioned between the inlet and reservoir. An air induction assembly may be attached to the packing tower or the inlet. A fuel gas line is in thermal communication with the reservoir. The fuel gas line has two ends a first end in close spatial relationship to a distal end of said reservoir, and a second end in close spatial relationship to a fuel output. Finally, a fluid conduit connects the second end of the fuel gas line and the water inlet.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority as a continuation-in-part of U.S. patent application Ser. No. 13/194,665, filed on Jul. 29, 2011, currently pending, which in turn claimed priority to U.S. Provisional Application No. 61/368,767 filed on Jul. 29, 2010, now expired.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to heater, furnace, and boiler flue-gas economizers, and more particularly, this invention relates to a system of recovering flue effluent heat within a closed loop to equalize the temperature of a fuel line.

2. Background of the Invention

Furnaces or boilers combust fuel to melt ore, heat air, dry wood, or cook food. These activities generate high-temperature effluent, such as flue gas. This effluent contains wasted heat energy.

“Economizers” attempt to re-capture heat from effluent.

For example, U.S. Pat. No. 1,795,909 to Brunt et. al. describes a series of complicated flue-gas passages, dust catching channels, and other convoluted physical structures designed to pre-heat air. The '909 patent relies on these structures to transfer heat from the flue gas to cold air. Consequently, Brunt uses a number of complex heat sinks. Further, Brunt admits that “dust-catching” means are required for particulate, inasmuch as build-up around the heat-sinks is a problem.

Another economizer is shown in U.S. Pat. No. 4,318,366 to Tompkins. This economizer includes dispersal of heat-trapping fluid in the flue-gas. However, the Tompkins system requires strict control of the temperature of flue-gas at several points, as well as single use and strict control of the temperature of the heat-trapping fluid.

A need exists in the art for a flue-gas economizer which is not complicated in design. The economizer should rely on inexpensive heat trapping media which is automatically recycled after it absorbs and releases energy. The heat trapping media should be the only moving element throughout the economizer.

SUMMARY OF INVENTION

An object of the present invention is to provide a device which eliminates many of the drawbacks of state of the art heat economizer systems.

Another object of the invention is to provide a means to extract and recycle heat from combustion effluent that would otherwise be released into the atmosphere. A feature of the invention is a heat exchange region in which reusable fluid transfers heat, via thermal conductance, from flue gas and then eventually to fuel. An advantage of the invention is that the fluid is not in fluid communication with the fuel, and as such, neither contaminates, nor is contaminated by, the fuel.

Still another object of the invention is to maximize the efficiency of a boiler or a furnace charged with gas or liquid fuel. A feature of the invention is the use of a completely separate device to transfer heat energy from combustion flue-gas (which is generated by the boiler or furnace) to pre-combusted fuel so as to preheat the fuel. An advantage of the invention is that the preheated fuel feature increases the efficiency of the boiler or furnace as compared to if the fuel was not preheated

Yet another object of the present invention is to provide a flue-gas economizer which recycles heat exchange fluid. A feature of the economizer is that the heat transfer fluid is reused and confined within a recirculation loop so as not to contaminate or clog other aspects of the combustion system, such as fuel supply lines or effluent stacks. An advantage of the invention is that the economizer works independently of boilers, furnaces, and internal combustion devices generally.

A further object of the invention is to transfer energy from a heat exchange fluid to a pre-combusted fuel fluid. A feature of the invention is a jacket encircling a fuel gas line, where the jacket is adapted to receive the heat exchange fluid. An advantage of the invention is that it maximizes the surface area of contact between the fuel conduit line and the heat exchange fluid (thereby allowing for high rates of flow of heat exchange fluid) while preventing direct physical contact of the fuel to the heat exchange fluid.

Another object of the invention is to collect heat from large volumes of effluent emanating from a combustion process. A feature of the invention is that heat transfer occurs without constraining the volume of the effluent or increasing back pressure to the combustion process gas. An advantage of the invention is that it may be used in conjunction with high-pressure boilers and furnaces which expel large quantities of flue gas.

Yet another object of the invention is to increase the temperature of a fuel line before a change in fuel pressure. A feature of the invention is that it can be used to heat a fuel line before or after a reduction in fuel pressure. An advantage of the invention is that it is separate from a combustion system such that it can be situated intermediate the combustion system and the fuel supply line undergoing a pressure change. Another advantage is that residual heat from a combustion system can be utilized by the invention to prevent fuel lines from freezing.

Another object of the invention is to facilitate cleaning of the economizer. A feature of the invention is that a cleaning cycle may be operated to rid the system of waste product. An advantage of the invention is that the cleaning cycle may be operated at any time, even when the underlying boiler or furnace is operating.

Another object of the invention is to provide an economizer which may be used in conjunction with a natural draught burner. A feature of one embodiment of this invention is that a fan is used to create a pressure differential within the system. An advantage of the invention is that the burners of the natural draught burner are provided with sufficient air to support combustion.

A further feature of the invention is to provide an economizer where the life-span of any fan used within the system is maximized. A feature of one embodiment of the invention is that the fan does not contact any fumes. An advantage of the invention is that the lifespan of the fan is maximized inasmuch as the fan is not exposed to a caustic environment.

Yet another object of the invention is to provide an economizer which may be used with any kind of boiler or furnace without modifying the furnace. A feature of one embodiment of the invention is an air induction fan may be located at several alternate sites depending on the type of boiler attached thereto, removing the need to induce an air draught within the boiler itself. An advantage of the invention is that it does not require the addition of an air inducer into the furnace, by creating a stand-alone air induction unit within the economizer.

A further object of the present invention is to provide an economizer that preheats fuel for other industrial processes. A feature of the present invention is that the economizer can circulate fluid in one or more pipe jackets. An advantage of the present invention is that the captured heat can be used more efficiently to heat processes that can take better advantage of fuel preheating.

Another object of the present invention is to provide an economizer that preheats fuel for the attached heater and for another industrial process. A feature of the present invention is that the economizer circulates fluid in more than one pipe jacket. An advantage of the present invention is that fuel for multiple applications can be preheated to take advantage of the increased combustion efficiency.

Still another object of the present invention is to provide an economizer that captures waste heat from a heater's exhaust on a hydraulic fracturing tank. A feature of the present invention is that the hydraulic fracturing tank utilizes a fire tube to circulate heat in the tank. An advantage of the present invention is that the exhaust heat is used in the economizer to heat fluid in the fracturing tank. Another advantage of the present invention is that the captured heat energy can alternatively be used to preheat fuel in a fuel line.

Briefly, the invention provides a flue gas heat recovery device comprising: a packing tower adapted to receive a flue gas stream; wherein said packing tower contains at least one water inlet, a water collection reservoir and a packing tray positioned intermediate said water inlet and said reservoir; a fuel conduit in thermal communication with the reservoir, wherein the fuel conduit has a first end in close spatial relationship to a distal end of said reservoir, and a second end in close spatial relationship to a fuel output; and a fluid conduit having a first end in fluid communication with an exterior surface of the fuel gas line and a second end in fluid communication with said water inlet.

The invention also provides a method for recovering heat from flue effluent, the method comprising contacting the effluent with a heat transfer fluid for a time sufficient to transfer heat from the effluent to the heat transfer fluid; transferring heat from the now heated heat transfer fluid to a fuel gas so as to heat the gas and cool the heat transfer fluid; combusting the now heated fuel gas which leads to the production of additional flue effluent; and repeating the process using now cooled heat transfer fluid and additional flue effluent.

BRIEF DESCRIPTION OF DRAWING

The invention together with the above and other objects and advantages will be best understood from the following detailed description of the preferred embodiment of the invention shown in the accompanying drawings, wherein:

FIG. 1 depicts a cut-away side view of an economizer, in accordance with features of the invention;

FIG. 2 is a view of FIG. 1 taken along lines 2-2;

FIG. 3 is a cut-away side view of an alternate embodiment of an economizer, in accordance with the features of the invention;

FIG. 4 is a detailed view of FIG. 3 area 4-4 of one embodiment of the invention;

FIG. 5 is a cut-away side view of another alternate embodiment of an economizer, in accordance with the features of the invention;

FIG. 6 is a detailed view of FIG. 5 area 6-6 of one embodiment of the invention.

FIG. 7 is a schematic view of an economizer with a separate fuel source;

FIG. 8 is a schematic view of an economizer with a branching fuel source;

FIG. 9 is a schematic view of an economizer preheating fuel for a vaporizer;

FIG. 10 is a schematic view of an economizer with multiple fuel line jackets;

FIGS. 11A-C are depictions of economizers for use with frac tanks; and

FIGS. 12A-B depict an indirect water heater embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings.

Turning to FIG. 1, the device 10 broadly comprises a packing tower 30, disposed in a generally vertical position, and a heat transfer jacket 64 in fluid communication with said packing tower 30. In the embodiment shown, the heat transfer jacket 64 is positioned at approximately a 90 degree angle to the packing tower so as to be disposed in a generally horizontal direction. A recirculation pump 50 is connected to said heat transfer jacket 64.

Hot exhaust generated from a combustion process occurring in a furnace, heater, or boiler is directed to a first end 34 of the packing tower 30. While the packing tower 30 is filled with hot exhaust, a heat transferring fluid enters the second end (in this embodiment the top end) 35 of the packing tower 30 so as to be gravity-fed towards the first end 34 of the packing tower 30. As the heat transferring fluid traverses downwardly through packing media 32 positioned intermediate the first and second ends of the tower, the temperature of the heat transfer fluid is increased as it cools the hot exhaust permeating upwardly from the first end 34.

Upon draining or otherwise exiting the packing tower 30 through a means of egress or tower to jacket connection point 52, the heat transferring fluid enters and substantially fills the volume defined by an annular space created by an outer skin 63 of a heat jacket 64, and an exterior surface of a fuel conduit or line 66. This facilitates transfer heat from the now heated fluid to fuel traversing the conduit 66. Because the heated fluid directly contacts the line 66, the entire surface of the line 66 within the jacket 64 is contacted by the heated fluid. This increases the amount of heat transferred from the fluid to the line 66, ensuring efficient use of the captured heat. Following traversal of the heat jacket 64, the now cooled heat transferring fluid is pumped by the fluid or recirculation pump 50 back to the second end 35 of the packing tower 30 to be re-circulated through the packing tower 30 which contains tower packing media 32.

Packing Tower Detail

In one embodiment, the packing tower 30 comprises a cylindrical structure, although other shapes are envisioned. In one embodiment, the packing tower is the vertical exhaust or smoke stack of a production environment or the portion of a vertical smoke stack.

The second end 35 of the packing tower 30 incorporates an exhaust aperture 36. In the embodiment shown in FIG. 1, said exhaust aperture 36 is open to the atmosphere. Exhaust aperture 36 may further incorporate one or more means of attaching exhaust handling devices, such as particulate scrubbers, negative pressure means, such as exhaust fans, and the like (not shown) for downstream processing of exhaust.

The interior of the packing tower 30 contains a plurality of packing media 32. Said packing media 32 is disposed between the first and second ends of the packing tower 30. In one embodiment, the shape of said packing media is mostly cylindrical and/or other hollow geometric shapes with stamped protrusions on the inside. The stamped protrusions allow for maximum heat exchange between the packing media, the effluent permeating upwardly through the media and the heat transfer fluid permeating downwardly through the packing media. In one embodiment, the packing media elements are metallic in construction, having a diameter of about 1″ and being approximately 1.25″ tall. However, other sizes are envisioned to maximize heat transfer and control back pressure. In one embodiment, the packing media 32 is placed on a fabricated packing tray 37 made from expanded metal, which is sheet metal having diamond-shaped holes stamped there through leaving a grid of approximately ⅛ inch of material remaining. The size of the apertures formed in the expanded metal tray is selected so as to prevent packing media 32 from falling through said apertures.

The packing media 32 is designed to provide maximum surface area for heat exchange fluid to contact the packing media 32. The maximum surface areas also allow the packing media 32 to transfer heat from the hot exhaust inasmuch as maximum surface area increases the time that both exhaust and heat exchange fluid contact the packing media 32. However, the packing media 32 are not so dense as to inhibit the transit of the hot exhaust through the packing tower 30. In one embodiment, the packing media 32 weighs 13 pounds per cubic foot while dry. The weight and quantity of packing media is selected to compensate for pressure loss and to optimize heat transfer. Further, the packing media is arranged such that heat exchange fluid does not pool or collect in any typographical features of the packing media 32.

A heat exchange fluid nozzle 40 is disposed between the second end of the packing tower 30 and the packing media 32. In the embodiment of the device depicted in FIG. 1, the nozzle 40 is disposed in the middle of a horizontal plane which runs parallel to the exhaust aperture 36, so as to facilitate downward projection of the heat transfer fluid (such as water) onto the packing media 32.

In another embodiment, not shown, the nozzle 40 is attached to the side of the wall of the packing tower 30 such that the nozzle is not adversely affected by the hot exhaust traversing the packing tower 30. In yet another embodiment, also not shown, more than one nozzle is employed.

During operation of the device 10, heat exchange fluid (such as water) exits the nozzle 40 and percolates downwardly through or otherwise traverses the packing media 32. In the embodiment shown in FIG. 1, the heat exchange fluid is propelled by the application of pressure and also by action of gravity. In other embodiments, the heat exchange fluid is propelled solely by action of pressure. In yet other embodiments, only gravity is responsible for the percolation.

Disposed between the first end of the packing tower 30 and the packing media 32 is the hot exhaust inlet 20. In one embodiment, the hot exhaust inlet 20 is in fluid communication with the headspace of a combustion chamber, such as those chambers found in furnaces and boilers. As such, the inlet serves as a means of ingress of combustion effluent into the device 10. While in some embodiments of the invention, the device 10 is connected to immobile devices such as large-scale boilers, in other embodiments, the hot exhaust inlet 20 connects to a temporarily-installed device, such as a generator.

Positioned superior from the hot exhaust inlet 20 is a gas and fluid permeable packing tray 37. Said packing tray 37 suspends and otherwise holds packing media 32 in place above the region of the tower receiving the hot flue gas. As such, the tray suspends the media above the head space. The hot exhaust is therefore in contact with packing media immediately upon entering the packing tower 30.

In one embodiment, the internal surfaces 38 of the packing tower 30 are substantially smooth. In another embodiment, the internal surfaces 38 of the packing tower 30 define a series of corrugations or channels designed to maximize the heat transfer characteristics of the said tower walls. The channels further provide a means for anchoring the packing media 32.

In one embodiment, the exterior of the packing tower 30 is insulated to prevent heat loss to the outside environment.

Finally, at the first end of the packing tower 30, the tower to jacket connection point 52 forms a heat transfer fluid exit conduit which provides the drainage means or other fluid egress means to facilitate removal of heat transfer fluid from the tower to the heat transfer jacket 64 described below.

Transfer Jacket Assembly Detail

The transfer jacket assembly comprises a sleeve or jacket 64 encapsulating, a fuel line 66. Specifically, the transfer jacket 64 resembles a tube radially displaced around a fuel conduit such that longitudinally extending portions thereof encircle or otherwise encase exterior surfaces of the fuel line 66 to form an annular space. The encasement of the fuel line 66 results in a void defined by the annular space, a fluid means of ingress (which is the heat transfer fluid exit conduit or tower to jacket connection point 52) situated at a first end of the void and a fluid means of egress (such as a connection conduit to pump inlet 56) situated at second end of the void. Further, in one embodiment of the invention, the exterior of the transfer jacket 64 is insulated so as to prevent heat loss to the external atmosphere. However, the external surface of the fuel line 66 is not insulated allowing for heat exchange between the interior of the transfer jacket 64 and the interior of the fuel line 66.

In one embodiment, the fuel line 66 is downstream of a fuel distribution network. In such a network (not shown) large quantities of fuel are sent over long distances using high-pressure transmission pipes. In one embodiment, such high pressure pipes contain fuel gas at 1200 psi. Upon reaching an end point of the network, such as a township, or a private user such as an industrial facility, the fuel gas line pressure is lowered to a pressure (e.g., 80 psi) suitable for end users. If the fuel gas line is not heated before the change in pressure, the fuel line would freeze once the pressure is decreased. In this embodiment, the fuel line 66 is positioned in close spatial relationship to that portion of the distribution network that subjects the fuel to depressurization so that the flange is adapted to receive or mate with a valve (not shown) separating the high pressure line from the fuel line 66.

In another embodiment, not shown, the fuel line 66 receiving heat within the transfer jacket 64 is the high-pressure transmission pipe prior to the decrease in pressure. Inasmuch as the fuel in the high-pressure line receives the heat from the heat transfer jacket, upon decreasing pressure, the lower pressure line is not liable to freeze. However, in this embodiment, the high-pressure transmission pipe must be designed to withstand not only the high-pressure fuel, but also the heated high pressure fuel which increases the pressure within the high-pressure line.

Finally, in further embodiments, the fuel line 66 is the upstream line side of the heater, and alternatively on the downstream line side of the heater.

In one embodiment, a first end or fuel output end 60 of the fuel line 66 is connected to a fuel-using device such as a furnace or a boiler. A second end or fuel input end 62 of the fuel line 66 is connected to a distribution line, or a still pressurized municipal gas supply or a fuel tank (not shown). The device 10 is capable of using any fuel, so long as the fuel may be conveyed in a fuel line, such as the fuel line 66 depicted in FIG. 1. The fuel must be of a type capable of being heated safely via thermal conductance and without significant expansion so as to rupture the fuel line 66. Fuels that have been safely used with this system include liquefied petroleum gas, methane, propane, butane, and higher carbon fuels which are liquids.

Inasmuch as in one embodiment, fuel is consumed at the first end 60 and originates at the second end 62, the fuel moves towards the first end 60 and away from the second end 62, which is the direction shown by the arrow gamma (“Γ”) in FIG. 1.

The heat transfer jacket 64 comprises two ends, a first end and a second end, which correspond to the two ends 60, 62 of the fuel line 66. However, in at least one embodiment, the heat transfer jacket 64 does not completely encapsulate the fuel line 66 and therefore a gap exists between the first end of the fuel line and the first end of the jacket (as well as the second end of the fuel line and the second end of the jacket) wherein the fuel line 66 remains exposed. Such a gap allows for direct manipulation of the fuel line 66 and facilitates the connection of the fuel line 66 to either a furnace or a fuel source.

The heat transfer jacket 64 is connected to a depending end of the heat transfer fluid exit conduit 52, which as discussed supra resides inferior to the packing tower 30. Proximate to the second end of the transfer jacket 64 is a pump inlet 56. The pump inlet 56 connects the interior of the heat transfer jacket 64 to a recirculation pump 50. The recirculation pump 50 applies negative pressure on the inlet 56.

Consequently, heat transfer fluid is drawn from the second end 35 of the packing tower, through the heat transfer fluid exit conduit 52, and to the pump inlet 56. Therefore, as shown in the embodiment of FIG. 1, the heat transfer fluid will travel in the direction depicted by arrow omega (“Ω”).

0 Inasmuch as the direction of the fuel “Γ” is opposite of the direction of the transfer fluid flow “Ω” the amount of time that fuel will be in thermal communication with (separated only by a wall of the fuel line 66) the temperature transfer fluid will be maximized. Additionally, the countercurrent nature of the fuel and transfer fluid flow ensures that the maximum amount of heat will be transferred from the hot transfer fluid to the relatively colder fuel. The transfer fluid also fully envelopes and is in direct contact with the fuel line 66, further increasing the amount of heat transfer.

The packing tower 30, transfer jacket assembly, and the recirculating pump 50 are connected through a series of conduits or piping described below.

Connection Detail

The second end 65 of the heat transfer jacket 64 is in fluid communication with the second end 35 of the packing tower 30. The first end 34 of the packing tower 30 is in turn connected to the first end of the heat transfer jacket 64. Consequently, the packing tower 30 and the heat transfer jacket 64 define a continuous loop to facilitate cycling of the heat transfer fluid.

Heat transfer fluid such as water is introduced at the recirculation pump 50. Heat transfer fluid exits the recirculation pump 50 through the pump outlet 58 to be fed under pressure to the second end 35 of the tower. The pump outlet 58 is in turn connected to one end of external fluid conduit 46 which lies external to the tower 30. The heat transfer fluid then traverses the external conduit 46 to reach the second end of the packing tower 30. The external conduit 46 can take any shape such that the device 10 can be adapted to operate with any furnace and stack combination. However, in the embodiment shown in FIG. 1, the external conduit 46 includes one or more conduit connectors 48, which allow the conduit to closely follow the shape of the remaining components. In other embodiments, not shown, the external conduit 46 comprises a flexible hermetically sealed passageway. Said external conduit 46 need not be made from a heat resistant material.

The external conduit 46 joins an internal conduit 42 at a conduit junction 44. The internal conduit 42 is exposed to hot exhaust found within the packing tower 30. Depending on the type of fuel being burned, the hot exhaust may be caustic. Consequently, while the external conduit 46 need not be heat and corrosion resistant, preferably, the internal conduit 42 comprises a material that is both heat safe and not subject to corrosion. The internal conduit 42 terminates in the one or more nozzles 40, described above, or other fluid dissemination means, said means proximate the second end of the packing tower 30.

The first end (in this embodiment, the depending end) of the packing tower 30 terminates in the tower to jacket connection point 52. A tower to jacket connection valve 54 is disposed on the heat transfer fluid exit conduit 52 between the first end of the packing tower 30 and the heat transfer jacket 64.

The opposite end of the heat transfer jacket 64 is connected to the pump inlet 56. Consequently, once introduced in the system, heat transfer fluid will circulate same, except for loss through the exhaust aperture 36, when some of the heat transfer fluid is spirited away or otherwise removed by venting exhaust fluid such as cooled flue gas.

While the heat transfer fluid is intended to recycle through the device 10, the system may enter a state when excess fluid is circulating through the system causing a build-up of pressure within the tower. As shown in FIG. 2, a region of the tower interior near the packing tray 37 defines a secondary outlet 80, which functions as an overflow valve. Excess heat transfer fluid that cannot be accommodated by the tower to jacket connection point 52 will exit the system through the overflow valve. While in the embodiment shown, the secondary outlet 80 is shown to be open to the external environment, in other embodiments not shown, the secondary outlet 80 is connected to a collection container for disposal. Further, the heat transfer fluid exiting the secondary outlet 80 may be measured, and the measurement may be used to control the rate of flow of the recirculation pump 50. In instances where the heat transfer fluid is exiting the secondary outlet 80, the recirculation pump throughput is lowered or the pump may even be turned off to maximize heat transfer between the combustion effluent and the temperature transfer fluid. The secondary outlet also serves as a means of egress for liquid products of combustion or condensed products of combustion to exit the economizer. The secondary outlet 80 also allows excess moisture to exit the system. The temperature of the exhaust of the heater may be lowered enough for the moisture within the exhaust to condense and so additional water will be introduced in the tower beyond what was used to transfer heat from the exhaust. Nonetheless, the secondary outlet 80 should not result in emptying of the tower from all liquid such that and the economizer should stay substantially full of heat transfer fluid during its operation, such that secondary outlet 80 serves as the full-point of the device

The device 10 further includes a means to hermetically connect the furnace or boiler to the device 10. As shown in FIG. 2, the device includes a furnace inlet joining plate 82 and a fuel output join plate 88 which allow the device to be removably connected to the furnace or boiler at the first end 60 of the fuel line 66. The outward surfaces of the join plates 82 and 88 are designed to matingly receive opposing flange surfaces of the furnace exhaust connections and fuel inlet connections.

Operation Detail

In operation, at the start of the cycle, the heat transfer fluid is introduced into the recirculation pump 50. In one embodiment, the hot exhaust is introduced only once the tower is filled with the cooling liquid. The fluid is added so that it reaches the tower secondary outlet 80. In this embodiment, the water exiting the secondary outlet 80 signals the filling of the tower. In other embodiments, water continues to be added to the tower until a level-indication float (not shown) is triggered. Other embodiments are capable of functioning in “off duty” cycles where the cooling tower is not filled with water.

In one embodiment, the heat transfer fluid is water; however, other fluids may be employed and are selected to transfer heat efficiently from the exhaust passing through the packing tower 30. Such fluids can comprise substances with boiling points lower or higher than water.

Upon the introduction of the heat transfer fluid, the external conduit 46 is pressurized such that the fluid traverses the internal conduit 42 to charge the nozzle 40. In one embodiment, the external conduit is pressurized to 5 psi. While other pressures are possible and strict pressure control is not necessary, the external conduit should not exceed 30 psi of pressure. In one embodiment, the heat transfer fluid then exits the nozzle 40. In another embodiment, the nozzle 40 incorporates a heat sensor, such that heat transfer fluid does not exit the nozzle 40 until the hot exhaust contacts the nozzle 40.

Concurrently with the heat transfer fluid traversing the internal conduit 42, hot exhaust enters the device 10 through the hot exhaust inlet 20. The hot exhaust permeates the packing tray along with the packing media 32 held by the packing tray, and the exhaust moves upwardly towards the exhaust aperture 36 and away from the hot exhaust inlet 20. In one embodiment, the hot exhaust entering the device 10 through the inlet 20 ranges in temperature from approximately 375° F. to 900° F. As the hot exhaust contacts the packing media 32, the hot exhaust transfers some of its heat energy to the packing media 32.

Further cooling of the hot exhaust occurs when the hot exhaust contacts the heat transfer fluid exiting the nozzle 40 as the hot exhaust approaches the nozzle 40. The heat transfer fluid further decreases the temperature of the packing media 32.

Due to this heat exchange, the hot exhaust experiences a temperature decrease of as much as 90% before venting through the exhaust aperture 36. Inasmuch as the heat transfer fluid captures the heat from the hot exhaust, in one embodiment, the heat transfer fluid's temperature increases to approximately 150° F. as the heat transfer fluid reaches the packing tray 37, having exited the nozzle 40 and moved through the packing media 32 and packing tray 37, both of which are permeated with hot exhaust.

In an embodiment, the exhaust entered the device 10 through the hot exhaust inlet 20 at a temperature of approximately 400° F. Following the heat transfer process, the heat transfer fluid reached a temperature of approximately 150° F. after contacting the hot exhaust and packing media 32. In another embodiment, the heat transfer fluid was at approximately 70° F. prior to contacting the media.

While it is impossible to prevent all evaporation of the heat transfer fluid, in one embodiment, heat transfer fluid is added and re-circulated so that the exiting exhaust temperature is maintained to less than 120° F. In this embodiment, the evaporation rate is under 10%. Further, in embodiments where the exhaust temperature is maintained under about 95° F., the liquid gained from condensation of vapor contained in combustion flue gas will approximately equal the amount of evaporation from the direct contact with the exhaust. As such, the system recuperates any water loss from evaporation of the heat transfer fluid, so as to conserve water resources.

After the heat transfer fluid percolates downwardly through transverse apertures formed in the packing tray 37, it then exits the packing tower 30 through the tower to the heat transfer fluid exit conduit 52. The heat transfer fluid which enters the heat transfer fluid exit conduit 52 contains the heat energy from the hot exhaust and is therefore hot. This heat energy from the heat transfer fluid is transferred, via thermal conductance through the walls of the fuel conduit, to heat the fuel prior to combustion of the fuel.

The heat transfer fluid enters the jacket through the heat transfer fluid exit conduit 52 and contacts the fuel line 66 near the first end 60 of the fuel line 66. In an embodiment of the invented system which conserves energy costs, the fuel entering the system from the first end 60 of the fuel line 66 is not heated up or otherwise thermally pretreated. To the extent that the fuel within the fuel line 66 is from an underground source, such as buried municipal gas lines, the fuel and fuel line 66 are likely to be cold. Even in instances where the fuel originates from an above-ground source such as a truck or tank, the difference in the temperatures between the fuel and the heat transfer fluid will result in a cooling of the fluid to below 70° F. Given the amount of time the cooling fluid contacts the exhaust traversing the tower, in instances where the cooling fluid is below 70° F., the exhaust exiting the tower will be under about 90° F. With the exhaust exiting at that temperature, it is possible for the overall heater to run at high efficiency.

This exact temperature is not known and is not a critical design requirement. As long as the exiting exhaust temperature is under 120° F., the fluid temperature leaving the tower is the only required information to properly size the length and width of the fuel heat transfer jacket 64.

As the heat transfer fluid fills the inside of the heat transfer jacket 64, the heat transfer fluid contacts the exterior surface of the fuel line 66. Given the above difference in temperatures, the heat transfer fluid loses its heat energy to the fuel line 66 and to the fuel contained within the fuel line 66 via thermal conductance through the walls of the fuel line. The heat transfer fluid which exits the heat transfer jacket at the pump inlet 56 will approach equilibrium with the temperature of the fuel line 66 at the second end 62 of the fuel line 66. However, since the fuel at the second end 62 of the fuel line 66 has most recently entered the device 10, this fuel is at the lowest temperature given its recent decompression from distribution line pressures. Consequently, the heat transfer fluid will reach or approximate its equilibrium point as it exits the heat transfer jacket 64 through the pump inlet 56.

The heat transfer fluid which reaches the recirculation pump 50 is pressurized to between 5 psi to 30 psi and forced out of the pump outlet 58 starting the cycle again by traversing the external conduit 46.

At the end of the operation of the furnace or boiler, or when it is desirable to flush the system clean, the heat transfer fluid is collected. The fluid may be collected through several points, including at the recirculation pump 50. At the recirculation pump 50, the heat transfer fluid may be diverted away from the device 10 by directing the fluid to a secondary outlet (not shown) instead of the pump outlet 58. Alternatively, the tower to jacket connection valve may be closed. Given this eventuality the heat transfer fluid will congregate and exit the device 10 through the packing tray secondary outlet 80 depicted in FIG. 2.

In the event of loss of heat transfer fluid, it may be replenished by the introduction of additional heat transfer fluid at the recirculation pump 50.

The device 10 also allows for several points of control. If the hot exhaust exiting the exhaust aperture 36 is too cold, it is possible to decrease the flow out of the nozzle 40 through operation of a valve at a conduit junction 44. The valve may be automatically controlled, via thermostat, or hand-controlled. Similarly, if the fuel exiting the fuel line 66 at the fuel line first end 60 is still too cool, the rate of flow of the heat transfer fluid may be adjusted at the tower to jacket connection valve 54 such that the fluid flow is increased around the exterior of the fuel conduit.

Air Induction Assembly

Turning to the alternate embodiment of the economizer system depicted in FIG. 3, the fan blower alternate embodiment 110 depicted therein does not seek to transfer heat energy to boiler fuel. Instead, the principal purpose of the alternate embodiment 110 is to ensure that the connected boiler receives a sufficient oxygen supply. Providing a sufficient oxygen supply is especially important for boilers having natural draught burners which in normal operation—i.e. operation where the boiler is not connected to an economizer—rely on air supply from the stack to maintain the flame. If an economizer is introduced to the stack, the exhaust is cooled and does not rise out of the stack. The trapping of the exhaust prevents the draught from pulling in outside air to the boiler's burners starving same of oxygen.

The embodiment 110 shown in FIG. 3 is designed to use an economizer with a natural draught boiler or any other fuel burning appliance which requires air from the exhaust to maintain the flame at the burners. The economizer 110 comprises a packing tower 130 having a first end 134 and a second end 135. A hot exhaust inlet 120 extends from the packing tower 130 at a location intermediate the two ends 134,135. Preferably, as shown in FIG. 3, the hot exhaust inlet 120 is located one third of the length of the packing tower 130 from the packing tower first end 134 and two thirds of the length of the packing tower 130 second end 135.

The hot exhaust inlet 120 comprises a heavy duty metal conduit, in one embodiment. The hot exhaust inlet 120 must withstand high temperatures and pressures of boiler exhaust traversing the inlet 120. A hot exhaust inlet aperture 162 is defined within the inlet 120 to allow for removal of excess fluid from the inlet 120. In one embodiment, the excess fluid is drained by gravity; in another embodiment, a pump is reversibly attached to the aperture 162 to remove fluid. The hot exhaust inlet 120 is angled with the end closest to the packing tower 130 lower than the end of the inlet 120 which is connected to the boiler. Given the angle, should excess fluid build up in the packing tower 130, the fluid will not traverse the inlet 120. Such fluid forms due to the cooling action of the economizer on the exhaust. If the condensation from the exhaust or other fluid were to return to the burners via the inlet 120, the burner flames can be extinguished.

In yet another embodiment, the aperture 162 is also used for reversible mounting of sensors (not shown) and for other means of monitoring the presence of exhaust within the hot exhaust inlet 162. In one embodiment, a switch (not shown) is mounted within the aperture 162, said switch being connected to the blower fan assembly 180 described fully below.

As the hot exhaust exits the inlet 120 and enters the packing tower 130, it contacts the overflow lines 160. The overflow lines 160 are connected to the packing tower 130 at the upper overflow aperture 161 near at the first end 134 of the packing tower 130. In one embodiment, the side of the packing tower incorporates a sight gauge tube 165 comprising clear tubing connected to the lower aperture 163 and the upper aperture 161. The sight gauge tube 165 allows for viewing of the level of liquid build-up within the packing tower 130. Any excess fluid that builds up within the packing tower 130 will fall down due to gravity towards the first end 134 of the packing tower 130. Initially, such fluid will exit the packing tower by being directed through the lower 163 aperture to the external sight gauge tube 165. However, if the amount of fluid becomes critical, and at the level of the exhaust inlet 120, the excess fluid will also exit through the upper aperture 161. In one embodiment, when the condensed exhaust fluid exits from the upper aperture 161, a sensor is triggered, indicating excess fluid in the packing tower 130. In another embodiment, when the fluid exits the upper aperture 161, the economizer cycle is slowed down by directing less exhaust through the inlet 120. Any fluid exiting the upper overflow aperture 161 is directed by the overflow lines 160 away from the device 110. The overflow lines 160 are angled to prevent the fluid from exiting the economizer in multiple directions.

After the hot exhaust enters the packing tower 130, the hot exhaust moves away from the first end 134 of the packing tower 130 towards the second end 135 of the packing tower 130. The interior of the packing tower between the inlet 120 and the second end 135 contains packing media (not shown). The packing media is inserted and removed by accessing the interior of the packing tower 130 via the packing media access portal 164. During operation of the economizer 110, this portal is sealed; however, if any of the media becomes deformed and is no longer able to function, it can be replaced by accessing the interior of the packing tower 130 through this access portal 164.

The packing media is cooled by being showered by a heat exchange fluid exiting the nozzle 140. The nozzle 140 is connected to the exterior of the packing tower 130 via an internal conduit 142. The internal conduit is in turn connected to an external conduit 146. In one embodiment, both the internal conduit 142 and the external conduit 146 comprise the same material; in other embodiments, the two conduits are made of different material, with the external conduit 146 being made from a less resistant material given that it is not exposed to the exhaust within the packing tower 130.

The external conduit 146 is connected to a cold fluid inlet (not shown). In one embodiment, the cold fluid inlet is connected to a heat transfer jacket, as was shown in FIGS. 1 and 2. In another embodiment, the cold fluid inlet is connected to a fresh supply of cooled fluid, such as a cold water line or a cooling body of water.

As the fluid exits from the nozzle 140, it traverses the packing tower 130 towards the first end 134 of the tower 130. The flow rate of the fluid out of the nozzle 140 is set based on the stack temperature read by temperature sensor 172. During operation, the fluid rate is set to maintain a constant temperature at 172 so that any water captured from the combustion process will be evaporated. The flow rate will vary to maintain this temperature by changing the speed of the pump 150.

As can be best seen in FIG. 6, fluid from the packing tower 130 is collected and conveyed to the recirculation pump 150 via the pump's inlet 156. The inlet 156 is connected to the packing tower 130 via a pump to packing tower connection pipe 270. The pump to packing tower connection pipe 270 is in fluid communication with the first end 134 of the packing tower 130. In the embodiment shown in FIG. 6, the pump to packing tower connection pipe 270 is closer to the first end 134 than the lower aperture 163. Therefore, fluid will not reach the lower aperture 163 except unless insufficient quantity of fluid is being conducted from the packing tower 130 via the pump to packing tower connection pipe 270. In one embodiment, if fluid is detected to have exited the lower aperture 163, the pump 150 output is increased.

The recirculation pump 150 forwards the heat exchange fluid under pressure to the pump outlet 158. The pump outlet 158 is connected to a heat exchange jacket as shown in FIGS. 1-2 or other heat exchange means, such as an outdoor fluid cooling body. In another embodiment, the output of the recirculation pump 150 is discarded.

After passing over the fluid exiting the nozzle 140, the exhaust exits the tower 130 by means of an exhaust aperture 136 located at the second end 135 of the tower 130. The aperture 136 provides for fluid communication between the tower 130 and the economizer exhaust stack 170. As the exhaust enters the exhaust stack 170, it has been considerably cooled by the packing media and the heat exchange fluid from the nozzle 140. If the exhaust has begun to condensate, fluid will fall down the packing tower 130 towards the first end 134. A temperature sensor 172, measures the temperature and rate of exhaust exiting the second end 135 of the packing tower 130 and adjusts the fluid flow of the nozzle 140 to prevent excess condensation given the likely make up of the exhaust.

An air induction unit, described below, is also connected to the exhaust stack 170.

Induction Unit

In the embodiment shown in FIG. 3, the air induction unit is connected to the economizer exhaust stack 170. In the embodiment shown in FIG. 5, the induction unit is connected to the inlet 120. The placement of the induction units at either location ensures that sufficient air is introduced into the system to maintain combustion within the boiler.

The induction unit comprises two components, one internal to the exhaust stack 170 and another exterior to the exhaust stack 170. The interior assembly comprises a pipe having two segments, a straight segment 174 and a curved segment 176. The straight segment 174 has a first end which is open while the second end of the straight segment 174 is connected to the curved segment 176. The curved segment 176 in turn is connected to the external assembly. The straight segment 174 is enclosed by the exhaust stack 170. The straight segment 174 is parallel to the exhaust stack, such that the interior 175 of the straight segment is concentric to the exhaust stack 170, as depicted in FIG. 4.

While as shown in the cut-away view of FIGS. 3 and 4, the straight segment 174 and the economizer exhaust stack 170 are substantially cylindrical in shape, other shapes may be used in other embodiments. In another embodiment, not shown, a rectangular vent is used for the exhaust stack 170.

The introduction of pressurized exterior air to the interior 175 of the straight segment 174 creates a pressure differential between the interior 175 of the straight segment 174 and the interior 177 of the exhaust stack 170. In one embodiment this pressure differential is set according to the boiler burner type and emission requirements. The pressure differential causes a partial vacuum to form in the interior 177 of the exhaust stack 170 surrounding the straight segment 174. This vacuum pulls air in from the outside of the exhaust stack 170 down through the exhaust stack 170 to the packing tower 130 and eventually to the boiler via the inlet 120.

The change in pressure in the straight segment 174 originates with the blower fan assembly 180 connected to the curved segment 176. The blower fan assembly 180 comprises a blower motor 182. The motor 182 operates a fan (not shown) which draws air in from the exterior of the economizer 110 through an air intake in the blower fan assembly 180.

Inasmuch as the fan draws exterior air into the curved segment 176, the fan does not contact the potentially caustic exhaust contained within the exhaust stack 170. Therefore, the fan does need not comprise durable materials. In one embodiment the amount of air the fan introduces into the stack per minute is set to meet boiler burner air needs and any emissions requirements. In one embodiment, the fan speed is kept constant throughout the operation of the system. In another embodiment, the fan speed and resulting output is automatically calculated and set on the basis of the exhaust sensor attached to the hot exhaust monitor aperture 162. In another embodiment, the fan is automatically turned to full speed as soon as exhaust is detected within the system. In yet another embodiment, the speed of the fan is set by the temperature of the flames within the boiler, said temperature being an indication of whether the flames have sufficient air.

The life span of the fan within the fan assembly 180 is maximized in this embodiment inasmuch as the fan does not contact the cooled exhaust and the condensate products within the exhaust. The condensation is instead collected and removed at the first end 134 of the packing tower 130. A fan connected directly to the humid environment of the packing tower 130 would suffer from the effects of contact the caustic environment.

Exhaust Intake Cooling

An alternate embodiment of the economizer is depicted in FIG. 5. The economizer 210 comprises a hot exhaust inlet 220 connected to a boiler (not shown) and a packing tower 230. The packing tower 230 used with this alternate embodiment 210 is analogous to the packing towers described above.

A testing port 262 is defined in the hot exhaust inlet 220 at a point along the length of the hot exhaust inlet between the boiler connection and the air induction segment 222. In one embodiment, a temperature gauge is connected to the testing port 262, while in another embodiment a combustion analyzer is connected at the testing port 262. In one embodiment, the combustion analyzer is used during setup or commissioning of the burner. During this setup phase, air and gas ratios are set to the proper amount, to ensure a clean burn. The analyzer is removed from the system after the setup is completed. During operation, temperature is measured to maintain the air mixture setting determined during the setup phase. In one embodiment, the hot exhaust inlet 220 air induction segment 222 is a stand-alone portion of the hot exhaust inlet 220 that can be connected to the hot exhaust inlet 220 in the event that the additional air supplied by the system is needed. In another embodiment, the induction segment 222 is integrally molded into hot exhaust inlet 220, but can be bypassed if not needed by closing the fan valve connection 223.

A fan assembly 224 is connected to the induction segment 222. The fan assembly comprises a fan 226, the fan housing 228, and the air introduction tube 232. In one embodiment, the fan 226 is protected by the fan housing 228, but at least one side of the fan 226 is exposed to the exterior atmosphere allowing the fan to draw in air from the atmosphere into the interior of the fan housing 228.

The interior of the fan housing 228 is connected to the air introduction tube 232. The fan valve 223 is found on the fluid connection between the fan housing 228 and the air introduction tube 232. In one embodiment, the fan valve connection 232 is automatically closed when exhaust is detected in the air introduction tube 232. Therefore, the fan 226 is protected from the hot exhaust in the inlet 220. If the fan is blowing air into the system, the valve 223 may be open inasmuch as the pressure of the air coming from the fan will push back and protect the fan from any returning exhaust. The exhaust will instead be directed to the packing tower 230 found at the opposite end of the inlet 220.

The air introduction tube 232 connects the fan valve 223 to the interior of the inlet 220. In one embodiment, a portion 234 of the introduction tube 232 is substantially parallel with the air induction segment 222 of the inlet 220. A connected portion 236 of the induction tube 232 turns approximately 90 degrees and becomes substantially perpendicular to the air induction segment 222.

When the fan 226 is turned on, air is forced from the external atmosphere into the fan housing 228. Inasmuch as the fan valve connection 223 is open, the air passes through the fan housing 228 to the air introduction tube 232 first the perpendicular segment 236 and then the parallel segment 234. The parallel segment 234 is open to the interior of the inlet 220. When the air exits the parallel segment 220, a partial vacuum is formed at the vacuum portion 238 of the inlet 220. The vacuum portion 238 surrounds the open end of the segment 228 between the exterior walls of the parallel segment 234 and the interior walls of the inlet 220.

The air added to the inlet 220 functions to decrease the temperature of the exhaust found in the inlet 220. A lower temperature of the exhaust allows the economizer to be used with high-temperature exhaust boilers. Further, the lower temperature of the exhaust allows for use of a cooling liquid other than water. In one embodiment, the cooling fluid comprises ethylene glycol or propylene glycol or a mix of either and water. The introduction of either ethylene glycol or propylene glycol allows the economizer to be maintained in a ready with all lines charged with cooling fluid, even when the economizer is shut down in climates where freezing occurs. These liquids would not be feasible or safe to use if the exhaust was of a high temperature.

The speed of the fan 226 is adjusted depending on the amount and temperature of the exhaust in the inlet 220. A temperature and pressure sensor 240 is located on the length of the air induction segment 220 between the boiler connection and the fan assembly 224 connection.

Other Preheater Embodiments

In other embodiments, the economizer preheats fuel for other industrial processes. In many settings, the amount of fuel required to operate a fluid heater, boiler, or furnace will be much less than the amount required to run other industrial processes within the facility. In these situations, preheating the fuel used in the industrial process is more beneficial than only preheating the fuel for the heater.

In each of these embodiments, the economizer 310 is similar to the previous embodiments in that it contains a tower 330 filled with packing media 332, an exhaust aperture 336, a permeable packing tray 337, and a nozzle 340. Further, the economizer 310 operates in same way as the previous embodiments; namely, it uses hot exhaust gases from a heater 345 to warm a circulating fluid. The warmed fluid is circulated through a jacket 364, which surrounds a fuel line 366. These designs also feature the countercurrent flow pattern and provide direct contact between the warmed fluid and fuel line 366, thereby maximizing heat transfer from the warmed fluid to the fuel.

In one embodiment depicted in FIG. 7, two separate fuel lines are used. A first fuel line 366 a supplies fuel to an industrial process 370. A second fuel line 366 b supplies fuel to the heater 345. Here, because the industrial process utilizes more fuel, efficiency is increased by preheating the fuel for that process instead of preheating fuel for the heater. This approach is also cost effective in some circumstances. For instance, the heater could be powered with relatively inexpensive natural gas, while the industrial process could be powered with relatively more expensive propane or LP Gas. By preheating the fuel for the industrial process, the efficiency of that process is increased, which means that a lesser amount of the more expensive fuels are used.

In another embodiment, the fuel line 366 splits into a plurality of branches 368 after passing through the jacket 364. Each branch supplies fuel for a different process. As can be seen in FIG. 8, the fuel line 366 splits into a first branch 368 a and a second branch 368 b. Because the heater 345 consumes less fuel than the industrial process 370, operating concurrently, the first, larger branch 368 a supplies fuel to the industrial process 370, and the second, smaller branch 368 b supplies fuel to the heater 345 for operation. The industrial process can be any of a variety of processes that take place in a plant or factory or on a job site for which hydrocarbon fuels can be used. Some examples of industrial processes that can benefit from this and the following embodiments are hydrate prevention in gas pipelines, propane vaporization, and pre-heating fuel for gas turbines.

In still another embodiment, shown in FIG. 9, the fuel line 366 is warmed in the jacket 364, and then it enters a vaporizer 372. The vaporizer can be a direct or indirect vaporizer. A direct vaporizer burns a portion of the fuel that is to be vaporized. An indirect vaporizer burns fuel from a secondary source. The embodiment shown in FIG. 9 depicts an indirect vaporizer. A first fuel from a first fuel line 366 a is warmed in the jacket 364 before entering the vaporizer 372. The first fuel is burned to heat a second fuel from a second fuel line 366 b. Often, the first fuel is natural gas and the second fuel is propane. As depicted in FIG. 9, the vaporized fuel from the vaporizer 372 fuels both the heater 345 and an industrial process 370. However, the fuel for the heater 345 could instead come from a third fuel line, and therefore, all of the output of the vaporizer 372 would fuel the industrial process.

In further embodiment shown in FIG. 10, the economizer 310 diverts warm circulating fluid into a plurality of jackets 364. At least one of the jackets 364 a surrounds the fuel line 366 a, leading to at least one industrial process 370. One jacket 364 b surrounds a fuel line 366 b that powers the heater 345. Different fuels can be carried in each of the plurality of fuel lines, or the same fuel can be carried in the fuel lines. Further, the relative size of the fuel lines can vary depending on the fuel needs of the process being fueled.

Hydraulic Fracturing Embodiment

In a specific application of the present invention, an economizer is used in conjunction with hydraulic fracturing equipment. Hydraulic fracturing, or “fracking” as it is commonly known, is a method of extracting hydrocarbon fuels from within underground rock formations. During fracking, pressurized water is pumped into a wellbore, which opens thin cracks in the rock formations. The water contains proppants, such as silica sand, resin-coated sand, ceramics, or a combination thereof. When the water is removed from the well, the proppants hold the cracks open so that the fuels can seep into the wellbore where the fuels can be collected.

The water used in fracking needs to be sufficiently hot to mix the fracking chemicals, to reduce the fracking fluid viscosity, or for other proprietary reasons. Typically, fracking fluid ranges from approximately 80° F. to temperatures of 185° F. or more. Since fracking is commonly done in remote, undeveloped areas, the heating of the fluid needs to be done onsite. Onsite storage and heating tanks, or frac tanks, are used to provide the heated fluid.

In this embodiment, an economizer 410 is used in conjunction with a heater 415 and a frac tank 420.

The frac tank 420 is a large, hollow structure used for storing and heating the fracking fluid. As depicted in FIGS. 11A-C, the frac tank 420 is rectangular in shape, featuring a distal end 421 d and a proximal end 421 p, a first sidewall 422 a and a second sidewall 422 b, and a top 423 and a bottom 424. However, other shapes can be used, including cylindrical tanks or pools of various polygonal perimeters. The embodiments of frac tanks shown in FIGS. 11A-C are mobile, and so, they feature a set of rear wheels 425 and a truck receiving assembly or mount 426; although, these features are optional for the purposes of the present invention.

The heater 415 is a combustion tube heater. The heater 415 can be powered by such fuels as natural gas, methane, propane, LP Gas, diesel, or combinations thereof. The combustion of these gases in the heater 415 produces hot exhaust gas that is ejected into a fire tube 427, which is a conduit through which the hot exhaust gases flow. As shown in FIG. 11A-C, the hot gases flow along a U-shaped path near the bottom 424 of the frac tank 420, starting at the proximal end 421 p near the first sidewall 422 a, flowing towards the distal end 421 d, and returning to the proximal end 421 p near the second side wall 422 b. While a U-shaped configuration is used in FIGS. 11A-C, other configurations are also suitable.

The fire tube 427 has an outlet 428 on the proximal face 421 p of the frac tank 420. The outlet 428 is in fluid communication with the economizer 410. The economizer 410 has the same basic structure as the previous embodiments, including a tower 430 filled with packing media 432, an exhaust aperture 436, a permeable packing tray 437, and a nozzle 440. The hot gases exit the outlet 428 into the lower region of the economizer 410, rise through the packing tray 437 and packing media 432, and vent through the exhaust aperture 436. Fluid is sprayed through the nozzle 440 onto the packing media 432, which has been heated by the exhaust gases. As the fluid percolates through the packing media 432, it is heated through the direct contact of the fluid with the hot packing media 432. The heated fluid collects in the lower region of the economizer 410.

In one configuration of the fracking embodiment shown in FIG. 11A, the fluid that is sprayed through the nozzle 440 is drawn directly from the frac tank 420, and the heated fluid in the lower region of the economizer is reintroduced to the frac tank 420. In this way, the economizer helps the fire tube 427 to directly heat the water in the frac tank 420.

In another configuration of the fracking embodiment as depicted in FIG. 11B, the heated fluid in the lower region of the economizer 410 is circulated through a first conduit 442 to a heat exchanger 445. A second conduit 447 carries fluid from the frac tank 420 to the heat exchanger 445. There, the fluid in the conduit 447 is heated by the heated fluid from the economizer 410. The warmed fluid from the frac tank returns to the frac tank via a first return line 449. The cooled fluid from the economizer returns to the economizer via a second return line 451. In this configuration, the fluid in the economizer is in a closed loop. Since some fluid will evaporate with the exhaust gas, the fluid will have to be periodically replenished.

In yet another configuration of the fracking embodiment shown in FIG. 11C, the heated fluid in the lower region of the economizer is circulated through a transfer jacket 464. The transfer jacket 464 is designed to surround and preheat fuel in a fuel line 466. The fuel line 466 can supply fuel to a variety of fuel consumers. For instance, the transfer jacket 464 heats fuel in a fuel line 466 used by the heater 415, by an on-site generator, by well-boring equipment, or any other on-site, fuel-consuming device. Further still, the economizer can divert heated fluid to a plurality of transfer jackets 464, which would allow the economizer 410 to preheat the fuel in multiple fuel lines 464.

In still another configuration of the fracking embodiment, the economizer 410 diverts some heated fluid to a heat exchanger 445 and some heated fluid to one or more transfer jackets, such as the heat transfer jacket 464 shown in the figure. In this way, the economizer can preheat fuel for consumption and aid in the heating of the fluid in the frac tank 420.

Indirect Bath Heater Embodiment

In another embodiment of the present invention, the economizer is utilized with an indirect bath heater. In an indirect bath heater, a conduit carrying a heated fluid is placed in a tank, or bath, of a second fluid that is to be heated. The heated fluid is generated in a burner or boiler. The hot fluid is typically combustion gases when a burner is used and hot water when a boiler is used. The hot fluid in the conduit warms the fluid in the tank. The heater is considered “indirect” because the heat source does not directly contact the fluid to be heated.

In this embodiment, the economizer captures waste heat from a burner and uses it to heat fluid contained therein. The heated fluid flows through a heat transfer jacket to preheat a process fluid. The process fluid is further preheated in the heater tank by running at least a portion of the process fluid conduit through the tank. If the process fluid is fuel, a portion of the heated fuel can be used to power the burner.

As shown in FIG. 12A, an economizer 510 captures waste heat in the exhaust gases produced in a burner 512. The burner 512 is proximal to a tank 514, which is filled with a fluid 516. The exhaust gases produced by the burner 512 flow through a conduit, or firetube, 518. The temperature of the exhaust gases depends on the type of fuel being used. If natural gas or propane is used, the exhaust gases produced will be at a temperature of approximately 2,000° F. As the gases flow through the firetube 518, heat is transferred to the fluid 516 in the tank 514. The temperature that the fluid 516 in the tank 514 achieves will depend on a variety of factors, such as the type of fluid, the size of the tank, the size of the firetube, and the amount of fuel being consumed in the burner. In a preferred embodiment, the fluid 516 in the tank 514 is heated to approximately 150° F. However, different applications of the heater system may require different fluid temperatures or even that the fluid be boiled.

The first end 518 a of the firetube 518 enters the tank 514 through at least one of the sides of the tank 514. As depicted in FIG. 12A, the firetube 518 enters and exits through the same proximal side 514 p of the tank. Inside the tank 514, the firetube 518 extends to the distal side 514 d of the tank and then returns to form a U-shaped path. Other configurations could also be used, such as a series of coils or a serpentine pattern. Upon exiting the tank 514, the second end 518 b of the firetube is in fluid communication with the exhaust aperture 520 of the economizer 510.

In the present embodiment, the hot exhaust gases exit the tank and enter the economizer at a temperature of approximately 500° F. The exhaust gases rise vertically within the economizer 510 through the underside of a packing medium 522. While the gases are rising, a nozzle 524 sprays a fluid onto the topside of the packing medium 522. As the fluid falls and as the hot exhaust gases rise, heat from the exhaust gases is transferred to the fluid within the packing medium 522. The fluid in the economizer 510 achieves a temperature of approximately 120° F. The exhaust exits the economizer 510 at a temperature of approximately 100° F.

The heated, falling fluid collects in a reservoir 526. The reservoir 526 features an outlet line 528 leading to a heat transfer jacket 530. The heat transfer jacket 530 surrounds at least a portion of a process fluid conduit 532. The fluid in the heat transfer jacket 530 returns to economizer 510 via a return line 534. Flow of the fluid through the transfer jacket 530 may be assisted by use of a pump 536.

Flow through the heat transfer jacket 530 is designed to be countercurrent to the flow of the process fluid within the process fluid conduit 532. This ensures that the maximum amount of heat is transferred from the fluid in the heat transfer jacket 530 to the process fluid. Additionally, the fluid in the jacket 530 directly contacts and surrounds the process fluid conduit 532. This feature further enhances the amount of heat transfer from the heated economizer fluid to the relatively colder process fluid. In the described embodiment, the temperature of the heated economizer fluid is approximately 80° F. upon entering the return line 534.

The temperature of the process fluid prior to entering the heat transfer jacket will vary depending on local conditions and whether the process fuel conduit 532 is buried. The minimum expected temperature of the process fluid is approximately 40° F. If the process fluid in the conduit 532 enters the heat transfer jacket at 40° F., the temperature of the process fluid will be about five to ten degrees warmer upon exiting the heat transfer jacket 530, depending on the efficiency of the firetube 518.

In an alternate configuration, depicted in FIG. 12B, the fluid in the economizer 510 and the fluid in the heat transfer jacket 530 are in separate loops. In this configuration, a heat exchanger 538 is disposed between an economizer loop 540 and a heat transfer jacket loop 542. The hot fluid from the economizer 510 flows through the outlet line 528 into the heat exchanger 538. There, the heat is transferred to the fluid in the heat transfer jacket loop 542. The fluid from the heat exchanger 538 flows through the heat transfer jacket 530, heating the process fluid. A second pump 543 circulates the fluid in the heat transfer jacket loop 542. By using a heat exchanger 538, the fluid in the heat transfer jacket loop 542 can be something other than water, such as a water and glycol mixture. Thus, the configuration shown in FIG. 12B helps protects the heat transfer jacket 530 and the process fluid conduit 532 from freezing and corrosion.

In both of the embodiments depicted in FIGS. 12A and 12B, after the process fluid is heated in the heat transfer jacket 530, the process fluid conduit 532 enters the tank 514. As depicted in FIGS. 12A and 12B, the process fluid conduit 532 follows a U-shaped path, similar to the path of the firetube 518 (albeit entering and exiting on the distal side as opposed to the proximal side of the tank). In the tank 514, the process fluid is further heated by the fluid 516 in the tank 514. The process fluid will typically attain a temperature of at least 70° F. after exiting the tank 514; however, temperatures higher than 120° F. are not uncommon. If the process fluid is a fuel, a fuel line 544 can be split off from the process fluid conduit 532. In the embodiments depicted in FIGS. 12A and 12B, the fuel line 544 provides fuel to the burner 512, but the fuel line 544 could provide fuel for other applications as well. Additionally, more than one fuel line 544 could be split off from the process fluid conduit 532.

The indirect bath heater as described in this embodiment provides several advantages. First, because the water is only heated, not boiled, no specialized tank is required to hold the water. If the heater allowed the water to boil, then a pressure vessel would be required. Second, the fluid in the tank provides additional indirect heating of the process fluid. Indirect heating is preferable so as to avoid exposure of the process fluid to a flame or heating element. Third, the heat from the economizer heats the process fluid instead of being recirculated in the heater tank. This isolates the water in the economizer from the fluid in the heater tank. In this way, only the economizer contains parts wetted with water. Thus, those parts must be made of corrosion-resistant materials, such as stainless steel, which are relatively expensive. In this embodiment, the heater tank could be made from a relatively less expensive material, such as carbon steel.

Though the present embodiment has been described in terms of an indirect water heater, the arrangement of components, including the economizer, heat transfer jacket, and the path of the process fluid conduit, can be used with direct contact heaters or boilers as well.

As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property.

It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting, but are instead are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. 

The embodiment of the invention in which an exclusive property or privilege is claimed is defined as follows:
 1. A flue gas heat recovery device comprising: a packing tower adapted to receive a flue gas stream from a water heater; wherein said packing tower contains at least one water inlet proximal to the top of the tower, a hot water collection reservoir proximal to the bottom of the tower, and a packing tray positioned intermediate said water inlet and said reservoir, wherein the packing tray supports a mass of packing material; at least one pipe jacket, wherein each pipe jacket has a first end and a second end and the first end of the at least one pipe jacket is in fluid communication with the packing tower reservoir, wherein the hot water from the reservoir flows into the at least one pipe jacket, and wherein each of the at least one pipe jacket is adapted to receive a fuel conduit; and a recirculation pump with an inlet in fluid communication with the second end of the at least one pipe jacket and an outlet in fluid communication with the packing tower's water inlet.
 2. The device of claim 1, wherein the fuel conduit supplies fuel for the water heater.
 3. The device of claim 1, wherein the fuel conduit supplies for a separate industrial process and a second fuel conduit supplies fuel for the water heater.
 4. The device of claim 1, wherein the fuel conduit forms at least two branches after going through the pipe jacket and wherein one branch powers the water heater and another branch powers a separate industrial process.
 5. The device of claim 1, wherein the fuel conduit flows into a propane vaporizer after going through the pipe jacket.
 6. The device of claim 5, wherein the fuel conduit is carrying natural gas.
 7. The device of claim 5, wherein the propane vaporizer vaporizes propane for both the water heater and an industrial process.
 8. The device of claim 5, wherein the propane vaporizer vaporizes fuel for industrial processes other than the water heater and wherein the water heater has an independent source of fuel.
 9. The device of claim 1, wherein the at least one pipe jacket is two pipe jackets.
 10. The device of claim 9, wherein one pipe jacket receives a first fuel conduit that provides fuel to the water heater and wherein the other pipe jacket receives a second fuel conduit that provides fuel to an industrial process.
 11. The device of claim 10, wherein the first fuel conduit and the second fuel conduit carry different fuels.
 12. The device of claim 11, wherein the first fuel conduit carries natural gas and the second fuel conduit carries LP Gas.
 13. A system for holding and heating fluid used in hydraulic fracturing, said system comprising; a tank with a fluid inlet conduit and a fluid outlet conduit; a burner in fluid communication with a fire tube, wherein the fire tube is located on the interior of the tank; and an economizer in fluid communication with the fire tube outlet, the economizer comprising: a substantially vertical tower; a heated gas inlet located on the lower portion of the vertical tower; a fluid distributing spout located on the interior of the vertical tower; a plurality of packing media suspended intermediate of the heated gas inlet and the fluid distributing spout, wherein the plurality of packing media are located on the interior of the vertical tower; and a fluid reservoir in communication with the bottom of the vertical tower, wherein the fluid reservoir is below the heated gas inlet; a fluid outlet port proximal to the bottom of the fluid reservoir.
 14. The system of claim 13, further comprising a heat exchanger with a first loop in which heated fluid flows form the fluid outlet port through the heat exchanger and into the fluid distributing spout and a second loop in which fluid flows from the fluid inlet conduit through the heat exchanger and into the fluid outlet conduit.
 15. The system of claim 13, further comprising a pipe jacket, surrounding a fluid-carrying conduit; and a recirculating pump, wherein the heated fluid flows from the first outlet port through the pipe jacket and then through the recirculating pump to the first distributing spout, thereby heating the fluid in the conduit.
 16. A system for heating a process fluid, said system comprising: a fluid tank; a burner in fluid communication with a first end of a conduit, wherein the conduit is adapted to receive exhaust gases from the burner and wherein the conduit runs through at least a portion of the interior of the fluid tank; an economizer, wherein the economizer is designed to receive a second end of the conduit such that exhaust gases from the burner flow through the conduit and into the economizer and wherein the exhaust gases flow upwardly in the economizer and transfer their heat to downwardly flowing liquid within the economizer; a heat transfer jacket, wherein the heat transfer jacket receives heated liquid from the economizer; and a process fluid conduit, wherein at least a portion of the process fluid conduit is surrounded by the heat transfer jacket such that the hot liquid from the economizer directly contacts the process fluid conduit and warms the contents of the process fluid conduit and wherein at least a portion of the process fluid conduit runs through at least a portion of the interior of the fluid tank.
 17. The system of claim 16, wherein the process fluid conduit carries a fuel to be heated.
 18. The system of claim 17, wherein at least one fuel line splits off from the process fluid conduit at a point on the process fluid conduit after the process fluid conduit exits the fluid tank.
 19. The system of claim 18, wherein one of the at least one fuel lines supplies fuel to the burner.
 20. The system of claim 16, wherein the liquid in the economizer and the liquid in the heat transfer jacket are isolated from each other and wherein heat from the liquid in the economizer is transferred to the liquid in the heat transfer jacket in a heat exchanger. 